DIOCLETIAN, CAIUS VALERIANUS°, Roman emperor 284–305 C.E. Diocletian is mentioned in Jewish sources on various occasions, particularly in the Jerusalem Talmud, and despite their aggadic embellishments they appear to contain at least a kernel of historical truth. Thus the fact that he was of lowly birth, the son of a humble scribe or of a slave (Eutropius, Breviarium 9:19, 2), is embellished in the Talmud to the effect that in his youth he was a swineherd, and the pupils of the Nasi Judah II used to mock and beat him. When he became emperor he sought to revenge himself on the Jews and summoned Judah to appear before him. Judah answered that they had derided Diocletian the swineherd but not Diocletian the emperor (TJ, Ter. 8:11, 46b). It is known that Diocletian was in Palestine, and in Tiberias, both in 286, during the patriarchate of Judah II, and during his campaign against the Persians (297–8), and it is probable that he had contact with the leading Jews there. Similarly there is an echo of the heavy taxation which he imposed in Palestine in the story that the inhabitants of Paneas went into exile as a result of these taxes, and returned only after 30 years (TJ, Shev. 9:2, 38d).

Diocletian showed a certain tolerance toward the Jews, one of the reasons probably being that Judaism – unlike Christianity – had been declared a religio licita by the Romans. Thus, when he imposed a tax to provide sacrifices to the gods – a fact explicitly mentioned in the Talmud (TJ, Av. Zar. 5:4, 44a) – he excluded the Jews, but not the Samaritans, from this impost. The Jews reacted favorably to this treatment. It is stated that Hiyya b. Abba, who was a kohen, crossed a cemetery in order to meet him (TJ, Ber. 3:1, 6a). Shortly after his stay in Tiberias he issued an edict against bigamy (Cod. Just. 5:5, 2) and against a man marrying his niece, but they do not appear to have been applied to the Jews. The Talmud quotes an inscription which Diocletian inscribed when he dedicated a market place to Hercules (or Heraclius) in Tyre (Av. Zar. 1:4, 39d) and that he instituted waterworks in Syria. Evidence of his stay there is confirmed from the Codex of Justinian (14:41, 9).